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Elite Model 3002M

Kaufhof AG was in the 1970s of the largest department store chains in Germany, selling their products both through hundreds of brick-and-mortar stores and through catalogues. Starting in 1973, Kaufhof used the label Elite on desktop and handheld calculators manufactured by various Original Equipment Manufacturers (OEMs) in Asia, like Omron, Satek, Unitrex and TEAL.

Dismantling the featured Elite Model 3002M calculator manufactured in September 1975 in Japan reveals a very compact design based on a single-sided printed circuit board (PCB) for the main electronics, a single-sided PCB for the keyboard and powered by four disposable 1.5 Volts batteries or an external 6 Volt power adapter .

The Main-PCB is centered around a µPD276 single-chip calculator circuit manufactured by NEC and the few other remaining components on the PCB are mainly used to generate the different supply voltages for the µPD276 and Vacuum Fluorescent Display (VFD) and to bias the anodes and grids of the display with respect to its filament.

To gain some knowledge about the differences between the µPD276 located in this Elite Model 3002M and the µPD277 used with the MBO de Luxe III, we decided here at the Datamath Calculator Museum to give the featured calculator a full "Teardown Treatment" and share our findings accordingly.

Calculating Unit: The µPD276 located in the featured calculator seems to be an upgrade of the µPD277, one of the first "true" single-chip calculator circuits with 8-digit capability and integrated 2-key Memory designed by NEC. The µPD276 features a 3/4-key Memory with optional Auto-Summation Function and the Constant Function is extended from Multiplication and Division only and operates with Addition and Subtraction, too. The integrated clock oscillator is slighly improved and doesn't need an external resistor like the original µPD277. For both chips the segment and digit output drivers are interfacing directly with low-voltage VFDs up to 30 Volts. Here at the Datamath Calculator Museum we don't qualify NEC's earlier µPD271 as a true single-chip calculator circuit, it is using with the µPD261 an external segment decoder and driver chip for the calculator display.

Display: The featured Elite Model 3002M calculator manufactured in September 1975 makes use of an 9-Digit low-voltage VFD manufactured by Futaba and known as Type 9-CT-02, soldered with its 19 wires directly to the Main-PCB.

Display Driver: The term "low-voltage" Vacuum Fluorescent Display might be misleading when used together with a calculator powered by four 1.5 Volt batteries. Common VFDs used with portable electronic calculators are usually operated around 30 Volts, significantly higher than the 10 to 15 Volts operating voltage of single-chip calculator circuits used in the 1970s. While the first generation of Texas Instruments TMS0100 single-chip calculator circuits lacked any display drivers and left the choice of display technology to their customers, focused the second generation products mainly on Light-Emitting Diode (LED) technology. In or around 1974, most Western calculator designs still relied on rather expensive LED technology but Japanese companies like Casio, Sanyo, Sharp and Toshiba started to leverage the lower manufacturing costs of VFDs, instead. Texas Instruments introduced in 1974 consequently with the TMS0850 their first product series focused on battery operated VFD calculators and modified the integrated segment and digit output drivers to withstand up to -35 Volts. NEC on the other hand entered the marked of single-chip calculator circuits in 1973/1974 and focused immediately on compatibility with VFDs. The µPD276 and µPD277 chips are manufactured in PMOS technology, meaning the output transistors are "high-side" switching and the most positive voltage of the chip is labeled V_SS for 0 Volt, all other voltages in the calculator are consequently negative with respect to V_SS. Multiplexed low-voltage VFDs need a voltage difference between its filament and the grids and anodes of the numbers of around 30 Volts to light up and to avoid "ghosting" while scanning, the deactivated grids and anodes should be slightly lower than the filament voltage. An elegant and very common solution is found with this Elite Model 3002M calculator, too. The grids and anodes of the VFD are "pulled-down" with 17 resistors (100k Ohm) to around -28 Volts, the filament is biased to around -26 Volts (Zener Diode) and the µPD276 switches the relevant grids and anodes to around 0 Volt to lit them up.

Clock: The Elite Model 3002M makes use of the internal clock oscillator of the µPD276 single-chip calculator circuits, we identified a capacitor with 82 pF connected between Pin 28 (CLK/C_EXT) of the µPD276 and the V_SS power supply line resulting in a clock frequency of about 39 kHz. The resistor found with the MBO de Luxe and connected between Pin 28 (CLK/R_EXT, C_EXT) of the µPD277 and the negative V_GG power supply line was dropped from the Bill of Material of the calculator.

Power Supply: The Elite Model 3002M calculator is powered with four disposable AA-sized 1.5 Volt batteries or an external 6 Volt power adapter and uses a complex DC/DC converter to generate a total of four voltages:

We measured the operating current of the featured Elite Model 3002M calculator for two different cases:

Calculating the power consumption at 6 Volts for the Elite Model 3002M results in about 250 mW displaying a '0.' and about 310 mW with all segments but the minus sign illuminated. A very interesting result, a Canon LE-84 calculator with a LED display and using four disposable 1.5 Volt Alkaline batteries and a DC/DC converter for its TMS0801 chip, clocks in at around 100 mW displaying a '0.' and 320 mW with all segments lit; showing both an advantage and disadvantage of LED-based calculators versus their VFD-based counterparts:

Keyboard: The keyboard assembly of the Elite Model 3002M with the Date code 50.8.12 was manufactured by GICO in September 1975 and uses 24 spring-supported plastic keys pushing small fingers on stamped sheet-metal pieces against contacts etched on a single-sided phenolic PCB.

The µPD276 single-chip calculator circuit uses not only its 9 digit driver outputs D1 to D9 to scan the keyboard, it even includes a 10^th output D0 to accommodate up to 30 keys in a 10*3 keyboard matrix. The layout of the keyboard assembly of the featured Elite Model 3002M calculator shows consequently an arrangement with 10 keyboard scan lines and 3 keyboard return lines.

Here at the Datamath Calculator Museum we use the DCM-50A Platform to Characterize and Reverse-engineer Single-chip Calculator Circuits. Many designs of electronic calculators do not use all features of their calculator brains and it would be difficult to unleash the full potential of the calculator chips in these cases. Additionally are electronic calculators "closed systems" with limited flexibility to measure signals, change voltages or clock frequencies, provide additional input keys or even change the display technology or specifications additional digits. Core idea of the DCM-50A is providing a generic platform to access all features of a single-chip calculator circuit and with the DCM-50A (PLAYGROUND) we increased the scope from Texas Instruments products to offerings from their competitors in the 1970s, namely AMI, Cal-Tex, Commodore/MOS Technology, Electronic Arrays, General Instrument, Hitachi, Litronix, Matsushita, Mitsubishi, Mostek, National Semiconductor, NEC, Omron, RFT, Rockwell, Sharp, Toshiba, and Western Digital.

Comparing the Calculator Logic Implementation of the µPD276 harvested from the featured Elite Model 3002M with the Calculator Logic Implementation of the µPD277 from an MBO de Luxe III reveals some interesting differences:

If you have additions to the above article please email: joerg@datamath.org.

© Joerg Woerner, March 6, 2025. No reprints without written permission.